It is important that the colouring material for the colouring of hydrocarbons shall have a high drying power. As a matter of fact, the higher the dyeing power the smaller is the quantity of coloring material to be used, with a lower danger of possible deposits during storage and of residues of this colouring material in the engines.
The coloring material, in order that it may be used in the colouring of fuels, must satisfy various requirements.
(1) it must possess a high dyeing power; PA1 (2) it must have a sufficient solubility in the fuels with or without tetraethyl lead; PA1 (3) it must have a high degree of diffusion; PA1 (4) it must contain little or no produce insoluble in fuels; PA1 (5) it must leave only a minimum deposit of slags in the engine; PA1 (6) it must have a proper fastness to light under storage; PA1 (7) it must be compatible with additives, and shall not create combustion difficulties; PA1 (8) it must not be extractable from the fuel by treatment with water, acid or basic solutions; PA1 (9) it must be in a brittle but not powdery form, when in the solid form; PA1 (10) it must be sufficiently fluid to be solubilized in organic solvents, when in the liquid form. PA1 (a) easiness of use, PA1 (b) rapidity of metering, PA1 (c) a high diffusion coefficient, PA1 (d) the absence of powders. PA1 (11) a high concentration of dissolved dye of not less than 50% by weight with reference to the solution obtained; PA1 (12) a high fluidity; PA1 (13) no tendency of the dye to crystallize in the solvent; PA1 (14) stability of the liquid mixture at low temperatures over long periods of time; PA1 (15) low vapour tension of the liquid mixture in order to avoid the formation of crystalline clots which favor crystallization. PA1 aliphatic amines with 7 and/or 8 carbon atoms:0.35-0.50 mols PA1 aliphatic amines with 5 carbon atoms:0.40-0 mols PA1 aliphatic amines with 4 carbon atoms:0.25-0.10 mols PA1 aliphatic amines with 7 and/or 8 carbon atoms:0.45 mols PA1 aliphatic amines with 5 and/or 6 carbon atoms:0.35 mols PA1 aliphatic amines with 4 carbon atoms: 0.20 mols.
The use of the colouring material in the liquid form brings with it considerable advantages with respect to the powdery products, and this because of:
Anthraquinonic dyes used for the colouring of petroliferous products are quite known from the literature. (U.S. Pat. No. 2,211,943; U.S. Pat. No. 2,925,333; U.S. Pat. No. 3,164,449) but they hardly succeed in satisfying the above listed requisites and in particular the difficulties increase for the dyes used in the liquid form in which the colouring material, in order to be convenient from all points of view, must possess the following further requisites:
The use of anthraquinonic dyes as colouring material for fuels has always been limited because of their limited solubility in organic solvents.
The dyes of the anthraquinone series, known to be suited for the colouring of the fuels, show a solubility in a solvent of 10-20% by weight.
For higher percentages, of the order of 40-50% b.w., in the literature there may be found pasty products, of little or none fluidity, or also solutions with a 50%, resulting, however, at a more thorough examination, devoid of stability.